1973tr6 Posted July 28, 2015 Report Share Posted July 28, 2015 Suggestions please; The bike was running well when it was last used, I went into the garage to run it for a while and it starts OK but there is now a large flat spot when coming off idle. The motor stops firing and "bogs down", coming back the life about about 1/3 throttle. Opening the throttle very slowly helps a little, a little choke helps a little. I have had issues with the carb from day 1, overflowing every trial after about an hour but I had got that sorted . Here's what I have done: Emailed the OKO guys and they said look for an air leak. Stripped and cleaned the carb, blowing out all passages / jets etc. Checked the carb for air leaks Checked the rubber connector for cracks (it was new with the carb last fall) checked the inlet manifold to cylinder joint integrity. Checked the spark Replaced the main crank seals 6 months ago Things to check Cylinder base seal ? Replace the main seals again? Dump the OKO and fit a MIkuni ? Reset the float level (for about the 100th time?) The puzzle it that it was fine, nothing had changed and now it's not. Quote Link to comment Share on other sites More sharing options...
tony27 Posted July 28, 2015 Report Share Posted July 28, 2015 Check the o-ring on the air screw as a possibility for a air leak, may have dried out & shrunk from lack of use. Have never had that sort of issue with the Oko I've been using on my Sherco for the last 5 years but from stripping mine down I have noticed the o-ring on the airscrew. Some of the rebuild kits available on ebay have the o-ring equipped airscrew & some have 1 similar to the keihin which doesn't use a o-ring 1 Quote Link to comment Share on other sites More sharing options...
feetupfun Posted July 28, 2015 Report Share Posted July 28, 2015 Dont just blow out the jets. Remove the pilot jet and look through it and clean it until it is clear. Your symptoms sound like a blocked pilot jet. They commonly block up from either a particle or from gunk if you let premix dry out in the float bowl between rides 3 Quote Link to comment Share on other sites More sharing options...
bondy Posted July 28, 2015 Report Share Posted July 28, 2015 (edited) Throw it in the bin and buy a mikuni. Edited July 28, 2015 by bondy 1 Quote Link to comment Share on other sites More sharing options...
lbhbul Posted July 28, 2015 Report Share Posted July 28, 2015 It most certainly is not main seals, you have cleaned the carb and as above stated. I find WD 40 or similar thru the pilot circuit will leave a clear trail into the venturi to ensure visual clear passage. If you have not added/replaced the Femsa condenser with a remote under the tank I would encourage you to do so. Many have success with that carb. Good luck Quote Link to comment Share on other sites More sharing options...
sherpa325 Posted July 28, 2015 Report Share Posted July 28, 2015 (edited) Keihin / OKO style cabries don't have a fuel filter in the the carbie itself so its essential to fit an inline one particularly if you have a fiberglass tank. I fitted a keihin on mine years ago and am very happy with the result, so I bought an OKO off ebay which was very cheap to go on another bully, but could not get the thing to run at all. Basically it was a piece of rubbish, pulling it apart revealed there were no markings/ sizes stamped on any of the jets and no amount of blowing jets out or anything would get this thing running, you get what you pay for I guess. Cheers Greg Edited July 29, 2015 by sherpa325 1 Quote Link to comment Share on other sites More sharing options...
woody Posted July 28, 2015 Report Share Posted July 28, 2015 The OKO with no markings on the jets would be a Chinese copy, normally the chrome finish top to the carb is a distinguishing piece, there are one or two others. The jets are different shapes / style from proper OKO which uses Keihin jets and the main jet housing is different. The proper OKO is a decent carb, I have them on three Sherpas and an Ossa. All run fine. Usually they work straight from the box on most bikes and all I've done is move the needle one clip and alter the pilot as they come with a slightly rich pilot. I think all the bikes use the standard 112 main. I bought a Chinese version by mistake once and it's still on the shelf, couldn't get the Sherpa to run on it at all. Doesn't help when you don't know the jet sizes through having no markings either.... 5 Quote Link to comment Share on other sites More sharing options...
1973tr6 Posted July 29, 2015 Author Report Share Posted July 29, 2015 Thanks for all the advice, It is a Taiwanese, not Chinese carb complete with markings on the jets. I have stripped, blown, poked, immersed in solvent and WD40'd the carb until I am sick of it. It now knows its own way off the bike- I just stand there and whistle and it teleports from the bike to the workbench ;-) I have ordered a Mikuni today having finally given up. It is such a simple thing but so frustrating. What jets have users found work the best ? I am 500 ft above sea level. 1 Quote Link to comment Share on other sites More sharing options...
sherpated Posted February 21, 2016 Report Share Posted February 21, 2016 Im having the exact same problem on my 159 with a 28 mm oko. Did you get the mikuni on and working? Quote Link to comment Share on other sites More sharing options...
lbhbul Posted February 21, 2016 Report Share Posted February 21, 2016 (edited) Sherpated, First off where are you located? There will be good advise found here, but it really helps if we know where you are. The OKO carbs generally are OK and only need a little tuning, when you say "same problem", is it rich (smokey/burbly) or lean (gasps or dies)?These conditions are pilot jet size usually/air screw 1 1/2 turns out +/- 1/2 turn. Be sure pilot circuit is clean, does the bike start/idle OK? New spark plug. Do you still have the original Bing? Larry , Edited February 21, 2016 by lbhbul 2 Quote Link to comment Share on other sites More sharing options...
1973tr6 Posted February 27, 2016 Author Report Share Posted February 27, 2016 Sherpated, No I never got the OKO sorted. It is puzzling because the earlier issues I had with the carb, continually overflowing when the motor was warmed up, despite setting and re setting the float many times, were solved by replacing the float needle. The bike was running well one trial and then the next it was fine to start but quickly deteriorated, sounding like it was running too lean, then nothing... no start, no run. I cleaned and fiddled about with the F&%$^@ for weeks and finally gave in. Put on the Mikuni and voila.... not looked back since. The OKO is now in a box gathering dust. 1 Quote Link to comment Share on other sites More sharing options...
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